This invention relates to production of analogs of botanic seed wherein the genotype may be identical to the parental strain.
The conventional techniques of crop improvement in agriculture involve a search for strains of plants which exhibit new and useful characteristics, or refine and improve on existing ones. The search has evolved from mere selection of a desirable parent plant to hybridization between parental strains which each exhibit desirable characteristics to, finally, crossbreeding between homozygous strains such that identical F.sub.1 progeny will be produced in each subsequent crossbreeding.
The conventional methods of maintaining genetic identity are well known and described in the literature. See, e.g. R. W. Allard "Principles of Plant Breeding," (John Wiley and Sons, Inc., 1960). The maintenance of purebred strains and the repeated crossbreeding to obtain F.sub.1 progeny are time consuming and labor intensive.
An additional limitation on the sexual reproduction of parental strains has been the low seed productivity per plant. This often results from low vigour which is manifested by heavily inbred strains. Finally, only a relatively limited number of purebred lines may be produced, and this results in a decreased pool of genetic characteristics available for selection.
It has been recognized that some of these difficulties may be overcome by vegetative propagation of the parental strain. See: W. C. Anderson and J. B. Carstens, "Tissue Culture Propagation of Broccoli, Brassica oleracea (Italica Group), for use in F.sub.1 Hybrid Seed Production," J. Amer. Soc. Hort. Sci., 102(1), pp. 69-73 (1977). This technique avoids the problem of the change in parental strain genetic characteristics through sexual reproduction. However, the sexual cross to produce F.sub.1 seed does not guarantee uniform progeny where there is chromosomal trait segregation in the parental strains.
It has been suggested that a desirable species may be propagated vegetatively, and the somatic embryos or rooted plantlets produced thereby transferred to the field. However, this technique involves skilled labor in tissue culture laboratories, a transfer to a hot-house or nursery, and upon attaining sufficient acclimatization, a transplantation to the field. This procedure is costly and time consuming in comparison with the traditional methods of seeding.
To overcome some of these difficulties, the technique of fluid drilling has been developed. Fluid drilling methods have been used with pregerminated seed, e.g., D. Gray, "Comparison of Fluid Drilling and Conventional Establishment Techniques on Seedling Emergence and Crop Uniformity in Lettuce," J. Hort. Science. 53:23-30 (1978), and it has been suggested that fluid drilling may be adaptable to transfer somatic embryos directly to the field. D. A. Evans and W. R. Sharp, "Application of Tissue Culture Technology in the Agricultural Industry," in Application of Plant Cell and Tissue Culture to Agriculture and Industry, D. T. Tomes et al., eds. (University of Guelph Press, pp. 212-13, 1982). However, fluid drilling technology is capital intensive and requires the purchase of machinery and the development of new techniques in the agricultural community, which has been historically resistant to such change.
Thus, an object of this invention is to provide a technique whereby cultured plant tissue may be insulated from harmful conditions.
Another object of this invention is to decrease the time for raising a mature or vigorous seedling from meristematic tissue, somatic embryos or tissue-cultured plants.
Yet another object of the invention is to provide a medium to deliver the cultured plant tissue together with adjunctives facilitating seedling stand establishment.
A further object of the invention is to reduce the amount of handling between the development of the cultured plant tissue and its planting in the field.
A still further object of the invention is to reduce the need for special handling techniques and special technology during the development and growth of cultured plant tissue and, thus, overcome resistence to the introduction of new technology by adapting to existing methods of seed planting technology.
A final object of the invention is to provide a large scale, economical method to clone superior plants or hybrid plants.